Tip Region Research Articles

Structure and dynamics of a laminar separation bubble near a wing root: towards reconstructing the complete LSB topology on a finite wing

The influence of the wing root junction on the laminar separation bubble forming on the suction surface of a semispan NACA 0018 wing cantilevered from the wind tunnel test section wall is studied using surface flow visualisations, particle image velocimetry and surface pressure measurements at a chord Reynolds number of 125 000 and an angle of attack of 6 $^\circ$ . The test section wall boundary layer upstream of the wing is turbulent, and the spanwise influence of the junction on the separation bubble extends well beyond the test section wall boundary layer thickness. Substantial three-dimensionality is seen in the separation bubble flowfield near the wing root, where earlier transition and a reduction in separation bubble thickness is observed. In contrast with the wing tip, earlier transition and a reduction in separation bubble length occurs near the wing root. Outside of the junction affected region, the separation bubble is similar to separation bubbles forming on two-dimensional geometries, and displays mild spanwise waviness. The transition process away from the end affected regions is characterised by the formation of spanwise roll-up vortices that are shed in a nearly two-dimensional manner across the span. The analysis of the results shows that, near the wing root, the increased level of perturbations leads to earlier vortex roll-up and spanwise flow contributes to more rapid vortex breakdown. The results in the wing root region are complemented by the analysis of data from Toppings and Yarusevych (J. Fluid Mech., vol. 929, 2021, A39) in the wing tip region to provide a more holistic outlook on the laminar separation bubble topology and dynamics on the entire finite wing.

Aerodynamic Study on the Influence Mechanism of Bow Blades on the Flow Field of Supersonic Tandem Rotors

In order to research the influence mechanism of bow blades on the flow field of supersonic tandem rotors of compressors, the supersonic rotor rotor37 is taken as the prototype and redesigned as a supersonic tandem rotor. Compared with the prototype rotor37, the efficiency of the design tandem rotor is increased by 0.24% and the stall margin is increased by about 5.6%. Although the negative bow blade deteriorates the flow field in the tip region and the hub region, it significantly increases the efficiency and total pressure ratio of the tandem rotor from 20% span to 85% span. The efficiency of the design point of the tandem rotor with a negative bow angle of 10° is improved by 0.37%, and the stall margin is also increased to 20.71%. Positive bow blades improve the efficiency of the hub region and casing region of tandem rotors, but they significantly reduce the efficiency of the tandem rotor from 10% to 50%. The positive bow blade reduces the pressure ratio and efficiency at the design point and reduces the stall margin of the tandem rotor. The design point efficiency of the tandem rotor with a positive bow angle of 10° is decreased by 0.3%, the stall margin is decreased by 1%, and the mass flow of the design point is increased by 0.38%.

Numerical investigation of plasma actuator induced forcing direction on the performance of a low-speed isolated axial compressor rotor

This paper investigates the effects of changing the dielectric barrier discharge (DBD) plasma actuator forcing direction on stall margin improvement and aerodynamic performance of a low-speed axial compressor rotor. The effects of plasma actuator induced force at yaw angles of 0, +30, −30° relative to the rotational axis of the compressor were evaluated through the incorporation of body force spatial distribution into Navier-Stokes equation. The evaluations focused on compressor performance comprising rotor efficiency, total pressure rise coefficient, span-wise loss coefficient, and diffusion factor on one hand and the tip leakage flow structure on the other hand in each configuration. The results indicated that reduction of mass flow rate could be associated with rotor tip spillage and trailing edge backflow, leading to the occurrence of the stall phenomena and flow blockage in the rotor tip region. However, using plasma actuators led to the energized tip region flow structure and improved aerodynamic performance by reducing the size of the tip leakage vortex and flow blockage. Specifically, among proposed configurations, the forcing direction at a yaw angle of −30° improved the compressor stall margin by about 8%. This is mainly due to the higher plasma jet velocity in the relative frame of reference versus to other configurations resulting in higher injected momentum to the tip leakage flow. The results propose counter-flow induced forcing direction as a favorable configuration for stall margin improvement.

Control of Dynamic Stall on Swept Finite Wings

A low-amplitude high-frequency flow control strategy for mitigation of transient tip stall is demonstrated for the case of a finite swept wing using high-fidelity wall-resolved large-eddy simulations. A wing of aspect ratio and NACA 0012 section is considered at freestream Mach number and chord Reynolds number . The wing undergoes an oscillatory pitching motion with reduced frequency and angle of attack between and 22 deg, resulting in deep dynamic tip stall for the uncontrolled case. Spanwise uniform low-amplitude pulsed forcing is imparted through a zero-net mass flow blowing/suction slot located on the wing lower surface near the leading edge using both moderate and high frequencies, and 50, respectively. The imposed small fluctuations are amplified through the natural receptivity of the laminar separation bubble (LSB) and, in the case of the highest frequency, completely inhibit its bursting along the wing, which precludes outboard flow separation and subsequent dynamic tip stall. The lower-frequency forcing cannot overcome eventual bursting of the LSB near the wingtip; however, the resulting separation is localized to the tip region unlike the full outboard unloading of the uncontrolled case. Conditioning of the leading-edge flow through targeted manipulation of the LSB and its inherent dynamics maintained or enhanced the effectively attached flow throughout the pitching cycle, resulting in significant reductions in the cycle-averaged drag and in the force and moment excursions.

Vasculature of the Nasal Cartilage Region Related to Filler Injection.

A filler injection in the nose can be essential but is also dangerous, especially in the nasal cartilage region. To safely and accurately perform a filler injection, surgeons must have detailed knowledge of nasal anatomy. Associated the vessel branches and the characteristics of different nasal regions to provide suggestions for more suitable injection sites. Fifty specimens underwent computed tomography (CT) after contrast infusion. Qualified specimens were selected for 3D CT reconstruction. Dissection was performed to confirm the accuracy of the CT data. The branches of arteries with large diameters, the dorsal nasal artery (DNA) and the lateral nasal artery (LNA) were distributed within the superficial musculoaponeurotic system layer. The DNA was seen in only 58% of specimens. The artery crossed the midline over the upper lateral cartilage in 16% of specimens. The LNA was a constant branch that traversed the nasal tip. The LNA crossed the midline to the contralateral side in 18% of patients. We divided the nasal cartilage dorsum into two regions for easy handling: the supratip region (STR) and the nasal tip region (NTR). The branches distributed in the STR mostly originated from the DNA (81.6%, 40/49), while those in the NTR mostly originated from the LNA. The vasculature of the nasal cartilage region observed in this study is similar to that observed in previous studies. However, we found that the STR was an advantageous area for filler injection. At the same time, we provided suggestions for more suitable injection methods. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Transient nature of secondary vortices in an axial compressor stage with a tandem rotor

An efficient and compact design of a compressor continues to be a challenging area of research. The unavoidable streamwise adverse pressure gradient together with passage transverse pressure gradient restricts the maximum allowable blade turning. Tandem blading is an interesting concept for increasing the pressure rise by permitting a higher blade turning angle. The energized flow through the tandem blade nozzle gap helps to minimize the possibility of flow separation over the suction surface of the aft blade. However, a coherent transient analysis of a tandem rotor stage in an axial compressor is yet to be well explored. In the present paper, the complex flow field over a tandem rotor and the succeeding stator passage is analyzed in detail. Although the tandem rotor increases the flow turning and diffusion effect, the presence of separate trailing edge wakes and hub corner vortex causes early onset of flow separation over the stator suction. The flow structures developed within the rotor and the stator passages at different time instances are highlighted with the help of limiting streamlines and iso-surface Q-criterion superimposed with entropy contours. The results indicate that within the rotor passage, transient flow features are observed near the hub corner region close to the aft blade trailing edge rather than the tip region. When the rotor passes the stator leading edge, the rotor trailing edge leakage flow at the hub is entrained into the stator leading edge reverse flow region. This is then further circumferentially dragged into the mid-passage region. The interference of multiple rotor wakes with the stator leading edge leads to the formation of longitudinal and arch like separation vortices at the stator-hub and the stator-casing regions, respectively. These separation vortices grow in size while being convected downstream. Eventually, as time progresses, the vortices split and shed periodically from the stator surface. The present investigation highlights the requirement of a new stator design in a tandem rotor–conventional stator configuration. Such designs could further magnify the significant aerodynamic performance obtained using a tandem configuration.

Large-scale serial sectioning of environmentally assisted cracks in 7xxx Al alloys using femtosecond laser-PFIB

In order to better understand the mechanisms of environmentally-assisted cracking (EAC) of 7xxx aluminium aerospace alloys, large scale serial sectioning using the newly developed femtosecond laser plasma focused ion-beam (laser PFIB) has been performed on both AA7050 and AA7085 alloys containing environmentally-assisted cracks introduced during accelerated laboratory testing. The samples were firstly scanned using X-ray computed tomography in order to reveal the long-range crack morphology and allow for targeted lift out of the crack tip regions for serial sectioning. This paper describes the optimisation of the methodology for both the liftout procedure and subsequent serial sectioning using laser-PFIB. Electron backscatter diffraction (EBSD) mapping at each slice allowed for 3D reconstruction of statistically valid volumes of material, up to 0.5 mm3 with a fine voxel size (1 μm). High resolution secondary electron imaging at each slice allowed for 3D reconstruction of the crack volume, and the datasets were combined in order to investigate the interaction of the crack with the microstructure. Optimisation of both the liftout geometry and the slicing procedure resulted in significant reduction in laser-induced curtaining artefacts and higher quality data acquisition. For these alloys, laser slicing alone was sufficient to provide a deformation free surface allowing for EBSD indexing rates up to ~95% acquired at high speeds of ~2000 Hz leading to reasonable acquisition times of ~4–5 days for each dataset. The datasets have shown that the grains in these alloys are much larger and more complex than previously realised, and the interaction of these cracks with the microstructure have shown that complex-shaped recrystallised grains can lead to significant crack deflection in these alloys and so may help to explain the observed differences in EAC behaviour.

Fatigue crack growth in CNT-reinforced polymer composite

Carbon nanotubes (CNT)-reinforced polymer composite has many engineering applications due to attractive properties, like high strength to weight ratio. These materials are subjected to cyclic fatigue loading during their service life. This work proposed a dual scale modeling approach to predict fatigue crack growth behavior of CNT-reinforced polymer composite under the thermo-mechanical loading environment. The effective orthotropic property of CNT-reinforced polymer composite is estimated using the mean-field homogenization technique in meso-scale modeling. Further, the equivalent composite property is used for macro-scale fatigue crack growth study using higher-order extended finite element method. To present the efficiency of the proposed modeling approach, various combinations of polymer composite (by volume fraction of reinforcement at 7.5%, 10%, 12.5%, 15%, 17.5%, and 20%) are taken for analysis. At macro-scale modeling, XFEM with higher-order enrichment terms is employed to improve the solution accuracy at the crack tip region. The proposed computational approach has been employed with the in-house developed MATLAB code and DIGIMAT software. Several numerical examples are considered with geometrical discontinuities like multiple holes and cracks.

Numerical Investigation on the Performance of a Transonic Axial Compressor with Inlet Distortion and Low Reynolds Number

The performance and stability of the transonic fan stage with a nonuniform inflow is a key issue in aero engine operation, and the coupling of inlet distortion and low Reynolds numbers at high altitude creates more severe challenges to aero engines. This work used computational methods to explore the performance and stability of a transonic fan stage with inlet distortion and a low Reynolds number. To investigate this issue, the transonic fan stage NASA stage 67 with a 180° total pressure distortion at a low Reynolds number was selected as the test case. Full-annulus 3D unsteady simulations were conducted to reveal the details of the flow field under coupling conditions. The computational results under different conditions were analyzed and showed that the coupling effect was not linearly stacked with single factors. The low Reynolds number in the coupling case thickened the boundary layer on the blade surface, and, on the one hand, the profile loss in the hub region increased. On the other hand, the structure of shock wave was converted in the tip region, which increased the shock loss significantly. In addition, the variation in the shock wave structure reconstructed the pressure distribution on the blade surface, allowing the fluid to migrate to the tip region, which affected the tip flow structure and ultimately delayed the stability boundary.

Atomic-scale understanding of the structural evolution in TiN/AlN superlattice during nanoindentation—Part 2: Strengthening

The mechanical properties of superlattice (SL) TMN (transition-metal nitrides) coatings with different as-deposited structures are often quite different. These differences in mechanical properties can be attributed to distinct deformation and strengthening mechanisms. Here, we discuss the strengthening mechanisms of single- and poly-crystalline SLs under nanoindentation loads. We observe that the dislocation behaviors during nanoindentation, such as dislocation accumulation and crossing interfaces, are responsible for the strengthening of single-crystalline SL coating, whereas no such pronounced strengthening is observed in the polycrystalline SL. We further reveal the monoclinic phase transformation occurring at the SL, solid solution zone, and crack tip region in the single-crystalline coating. Phase transformation alters the SL interface's structure, facilitating dislocation accumulation. Consequently, it raises the theoretical yield stress of single-crystalline coating. For polycrystalline coating, we observed a localized monoclinic phase present only near the crack tip. The current research unravels TMN SL strengthening mechanism at the atomic scale.

Performance analysis of a horizontal axis ocean current turbine with spanwise microgrooved surface

The design of turbine blade is a vital issue in the performance of horizontal axis ocean current turbine (HAOCT). The purpose of this paper is to conduct the performance analysis for HAOCT blade with spanwise microgrooved surface, including hydrodynamic analysis and hydrodynamic noise analysis. To recognize the flow around the blades, and to obtain the radiated noise of the turbines, four turbines with different configurations of microgrooved surface are tested through computational fluid dynamics (CFD) method. The hydrodynamic characteristics are obtained based on large eddy simulation (LES), then Ffowcs Williams-Hawkings (FW-H) analogy is used to predict the rotating noise generated by the HAOCT. The accuracy of the numerical predictions of flow field is checked against existing experimental data, with good agreement achieved. The results indicated that the rational design of spanwise microgrooved surface could help to reduce the annoying hydrodynamic noise. Moreover, it is shown that the microgrooved surface in blade tip region has better noise reduction effect than that in blade root region. Nevertheless, the noise reduction effect is obtained at the cost of weakening the thrust and torque at a certain degree.

The influence of coal particle shapes on the interaction behavior of air bubbles and coal particles

ABSTRACT In order to study the influence of coal particle shape on the interaction behavior of air bubbles and coal particles, coal particles were divided into three types according to the contact region with air bubbles. They were angular coal particles (ARP) in point contact, prismatic coal particles (PCP) in line contact, and flat coal particles (FTP) in surface contact. Spherical coal particles (SLP) were used as a reference to compare the above three coal particles. We tested the acting time and force of coal particles with air bubbles using an instrument designed by us. For a systematic study, according to the angle of the contact location with the air bubble, the ARP and the PCP were subdivided into 5 types. By comparing the difference in the drainage time (DT) of the liquid film, the three-phase contact-line (TPCL) expansion time, the maximum repulsive force (MRF), and the maximum attractive force (MAF) during the acting process, the influence of the coal particle shape on the interaction process was systematically explored. The research results show that the order of DT, MRF, and MAF of the liquid film caused by the interaction of coal particles with bubbles is angular < prismatic < spherical < flat shape, while the order of TPCL expansion time is the opposite. As the angle of ARP and PCP increases, the DT, MRF, and MAF of the liquid film increase, the MAF of SLP and FTP are 54.50 μN and 104.99 μN, respectively, while the TPCL expansion time decreases with the increase of the angle. The MRF of SLP is similar to that of PCP of 120°, which are −43.42 μN and −41.84 μN, respectively. We further studied the adhesion and detachment processes. The results show that 95% of the coal particles will collide with the bubbles in thier sharp tip regions, and only 5% of the coal particles can collide with the bubbles in their plane regions when attachment is achieved. When the liquid film is induced to rupture, the irregularly shaped coal particles tend to contact the bubbles with their tips; when detachment occurs, the sharp tips of the coal particles will be dominant locations of detachment from the bubbles. Therefore, the shape of coal particles greatly affects the interacting process. This study provides a theoretical basis for effectively improving the flotation performance by changing the shape of coal particles in the process of coal flotation.

Effect of tip speed ratio on the aerodynamic noise of a small wind turbine: An optimization study

A dual-objective optimization study was carried out to illuminate how the tip speed ratio of a small wind turbine affects the aerodynamic noise as well as the blade geometry. A 0.75 kW three-bladed small horizontal axis wind turbine was selected as the case study. Two important goals were considered in the study: maximization of the output power and the minimization of the aerodynamic noise. The former was calculated by the well-known blade-element momentum theory while a validated semi-empirical model was adopted for the computation of the latter. A combination of these goals defined the objective function and the weighted-sum approach was employed to find the optimal values for the design variables of the optimization including the distributions of the chord and the twist angle along the blade together with the tip speed ratio. The extracted power was calculated at the rated wind speed of 10 m/s while the noise was computed at lower wind speeds of 5 and 7.5 m/s. The genetic algorithm technique was adopted for the muti-objective optimization. The results revealed the importance of the blade tip region in producing the emitted aerodynamic noise. Specifically, an increase in the chord and twist values near the tip results in the reduction in the emitted noise. Results also show that a good compromise between the two goals is achievable such that a noticeable reduction in the emitted aerodynamic noise is attainable in exchange for a very small drop in the power coefficient. The optimization results also indicated that the noise could be adequately reduced at the smaller value of the tip speed ratio without a large reduction in output power which is due to the decrease in the rotational speed of the turbine.

Effect of vorticity transport on flow structure in the tip region of axial compressors

Numerical simulations are carried out to investigate the flow structure in the blade tip region of axial compressors. Various tip clearance heights and end wall motion conditions in a linear compressor cascade are studied to assess the effect of vorticity transport on the tip leakage flow (TLF). Moreover, the effect of vorticity transport on the TLF in a compressor rotor at different operating conditions is studied using delayed detached eddy simulation. The results show that the vorticity transport at both the blade tip and the end wall plays an important role in the roll-up and evolution of the tip leakage vortex (TLV), resulting in great impacts on the loss and stability of the TLV. It is found that the TLV is composed of a two-layer structure. The inner vortex core region formed by the vorticity transport from the blade tip shear layer to the TLV has a great effect on the strength and loss of the vortex, and the structure of the outer shear layer is altered by the secondary vortex formed by the vorticity transport from the end wall shear layer and thus affects the stability of the TLV. By the mechanism of the vorticity transport, the effects of the clearance height, the end wall motion, and the non-uniform clearance as a control method can be explained uniformly. The new understanding of the TLF structure and the vorticity transport mechanism helps to improve the performance of axial compressors by controlling the vorticity transport of the TLF.

Study on the effect of rotor tip fillet edge in axial compressor

The compressor flowfield is sensitive to the small geometry in the tip region. The blade tip edge, which was usually idealized as “sharp” edge in the numerical simulation, had been actually filleted during the process of machining, coating, and wearing. However, the fillet edge was completely neglected in the compressor performance estimation. Thus, in this paper, the effect of the fillet edge is evaluated by establishing several models with tip fillet edges as well as tip sharp edge in a transonic axial compressor. By the comparison of the flowfield between models with fillet edge and sharp edge, it was found that the tip fillet edge can eliminate the separation bubble at the pressure side of the tip clearance. Also, it can affect the tip clearance outflow by changing the reversed flow. As a result, the leakage flow is increased and the compressor performance is decreased in efficiency and pressure ratio. The local leakage mass flow rate along the camber line can be increased up to 40% when the fillet radius is as much as 20% of the tip clearance size. The flowfield in the downstream is also affected by the fillet edge. By the comparing among the models with different working conditions, it is found that the sensitivity of the performance to the fillet edge is different between design and off-design conditions. Furthermore, the effect of the tip fillet edge on the leakage flow is qualified and compared with the effect of the tip clearance.

O-glycosylation of the extracellular domain of pollen class I formins modulates their plasma membrane mobility.

In plant cells, linkage between the cytoskeleton, plasma membrane, and cell wall is crucial for maintaining cell shape. In highly polarized pollen tubes, this coordination is especially important to allow rapid tip growth and successful fertilization. Class I formins contain cytoplasmic actin-nucleating formin homology domains as well as a proline-rich extracellular domain and are candidate coordination factors. Here, using Arabidopsis, we investigated the functional significance of the extracellular domain of two pollen-expressed class I formins: AtFH3, which does not have a polar localization, and AtFH5, which is limited to the growing tip region. We show that the extracellular domain of both is necessary for their function, and identify distinct O-glycans attached to these sequences, AtFH5 being hydroxyproline-arabinosylated and AtFH3 carrying arabinogalactan chains. Loss of hydroxyproline arabinosylation altered the plasma membrane localization of AtFH5 and disrupted actin cytoskeleton organization. Moreover, we show that O-glycans differentially affect lateral mobility in the plasma membrane. Together, our results support a model of protein sub-functionalization in which AtFH5 and AtFH3, restricted to specific plasma membrane domains by their extracellular domains and the glycans attached to them, organize distinct subarrays of actin during pollen tube elongation.

SEC1A is a major Arabidopsis Sec1/Munc18 gene in vesicle trafficking during pollen tube tip growth.

SUMMARYPollen tubes (PTs) grow by the targeted secretion of new cell wall material to their expanding tip region. Sec1/Munc18 (SM) proteins promote membrane fusion through regulation of the SNARE complex. We have previously shown that disruption of protein glycosylation in the Arabidopsis thaliana hpat1 hpat3 double mutant leads to PT growth defects that can be suppressed by reducing secretion. Here, we identified five point mutant alleles of the SM protein SEC1A as hpat1/3 suppressors. The suppressors increased seed set, reduced PT growth defects and reduced the rate of glycoprotein secretion. In the absence of the hpat mutations, sec1a reduced pollen germination and PT elongation producing shorter and wider PTs. Consistent with a defect in membrane fusion, sec1a PTs accumulated secretory vesicles. Though sec1a had significantly reduced male transmission, homozygous sec1a plants maintained full seed set, demonstrating that SEC1A was ultimately dispensable for pollen fertility. However, when combined with a mutation in another SEC1‐like SM gene, keule, pollen fertility was totally abolished. Mutation in sec1b, the final member of the Arabidopsis SEC1 clade, did not enhance the sec1a phenotype. Thus, SEC1A is the major SM protein promoting pollen germination and tube elongation, but in its absence KEULE can partially supply this activity. When we examined the expression of the SM protein family in other species for which pollen expression data were available, we found that at least one Sec1‐like protein was highly expressed in pollen samples, suggesting a conserved role in pollen fertility in other species.

Multi-Objective Optimization of Circumferential Groove Casing Treatment in an Ultra-Highly Loaded Low-Reaction Transonic Compressor Rotor

This study concerns a multi-objective optimization of circumferential single grooved casing treatment for a low-reaction transonic rotor with ultra-high loading. The axial location, width and depth of the groove are investigated as design variables. The optimization problem seeks to fully extend the operation range of the rotor while minimizing efficiency degradation. Artificial neural network of radial basis function is applied to construct the surrogate model. The optimal groove configuration was determined using non-dominated sorting genetic algorithm II (NSGA II) in conjunction with technique for order preference by similarity to ideal solution (TOPSIS). Detailed analysis of flow field reveals that two flow features involving stability enhancement for the low-reaction rotor are the inhibition of shock/vortex interaction in the rotor tip region and the reduction or elimination of double-leakage tip gap flow. The blocking region located right downstream of the interface between the tip leakage flow and the main flow is decreased due to the tip unloading effect and recirculation flow induced by the groove. Additionally, the efficiency improvement can be observed as the intensity of tip leakage vortex decreases. Based on the single groove optimization, the prospect of a particular multiple groove casing configuration consisting of component grooves with varied geometrical dimensions is also discussed in the paper. The simulation results indicate that the new-type multiple groove configuration is more advantageous to the rotor’s performance.

An Inverse Method for Wind Turbine Blade Design with Given Distributions of Load Coefficients

It is shown in the literature that wind turbine designs with different load distributions have different wake features. To systematically study how different load distributions affect turbine wakes, a method for designing variants of blades with different radial load distributions, but with approximately the same power (CP) or thrust coefficient (CT), is needed. In this work, an inverse design method based on the blade element momentum method and the multi-dimensional Newton’s method, with the normal and tangential force coefficients as the design objective and iterations for satisfying the CP or CT constraint, is developed. The proposed method is validated using the two-bladed small-scale NREL phase VI S809 wind turbine blade design and the three-bladed utility-scale NREL 5 MW wind turbine blade design. Four variants of the NREL 5 MW wind turbine, i.e., the Root-CP, Tip-CP, Root-CT, and Tip-CT designs, which represent the variants of the original design (NREL-Ori) with a higher load near the blade root and tip regions with approximately the same power coefficient (CP) or thrust coefficient (CT) as that of the NREL-Ori design, respectively, are then designed using the proposed method. At last, the flapwise blade bending moment and the power coefficients from different variants of the NREL 5 MW turbine are compared for different tip speed ratios, showing that the “Root” designs are featured by a wider chord near the root, lower blade bending moment, and higher power coefficients for tip-speed ratios greater than nine.

Cross-linkers at growing microtubule ends generate forces that drive actin transport.

SignificanceComplex cellular processes such as cell migration require coordinated remodeling of both the actin and the microtubule cytoskeleton. The two networks for instance exert forces on each other via active motor proteins. Here we show that, surprisingly, coupling via passive cross-linkers can also result in force generation. We specifically study the transport of actin filaments by growing microtubule ends. We show by cell-free reconstitution experiments, computer simulations, and theoretical modeling that this transport is driven by the affinity of the cross-linker for the chemically distinct microtubule tip region. Our work predicts that growing microtubules could potentially rapidly relocate newly nucleated actin filaments to the leading edge of the cell and thus boost migration.